Apparatus for scanning chromatograms and the like

ABSTRACT

Apparatus for scanning chromatograms and the like comprise stationary magnetized table, magnetized means for holding a sheet on the table, and means responsive to a property of said chromatogram which varies from point to point thereon, said means, being mounted to move parallel to the top of the table.

C United fies Pae 1 1 1111 3,777,363

Aubin et a1. 4, 1973 [541 APPARATUS FOR SCANNHNG CHROMATOGRAMS AND THELIKE [56] References Cited [75] Inventors: Guy Aubin, Saint Mande; AndreUNITED STATES PATENTS n' y; Jules Leroy, T893,011 12 1971 Hanggi et a1.250 435 MR x Vmeennes, all of France 3,116,416 12 1963 250 715 s X3,623,124 11/1971 P1atz.... 250/71.5 S X [73] Assgnee' L Urea" France3,200,252 8/1965 Moses et a1. 250/106 sc x [22] Filed: Jan. 21, 19723,033,986 5/1962 Fowler et a]. 250/83.6 PT

[211 App! 219638 Primary ExaminerArchie R. Borchelt Attorney.loseph A.Brisebois et a1. [30] Foreign Application Priority Data Jan. 29, 1971France 7102994 [57] ABSTRACT NOV. 30, i971 France 7142935 Apparatus forScanning chromatograms and the comprise stationary magnetized table,magnetized [52] US. Cl. 250/491, 23/254 R, 73/23.1, means for holding aSheet on the table and means 250/521 sponsive to a property of saidchromatogram which II.- Cl. varies from point to point thereon, saidmeans being [58] Field of Search 250/435 MR, 71.5 S, mounted to moveparallel to the top of the table 250/83.6 FT, 106 SC; 23/232 R, 232 E,254 R, 254 E; 73/23.1

24 Claims, 6 Drawing Figures PATENTEUUEE 4 ma SHEET 3 OF 4 FIG! 1 eAPPARATUS FOR SCANNING CHROMATOGRAMS AND THE LIKE It is conventional toprepare chromatograms on paper or on a thin layer of material in orderto separate the various constituents of a complex chemical composition.In some cases, when certain of the constituents thus separated on thepaper of a chromatogram are radioactive, it is necessary to accuratelydetermine the radiation emitted at each point on the chromatogram. It isthen necessary to move the chromatogram on the paper relative to aradiation counter of the Geiger type. The same problem occurs whenchromatograms are made on a thin layer of material, it being understoodthat this thin layer is made of a material which permits the separationof the constituents of the composition to be studied and replacesthe'paper of chromatograms made on paper.

lt has already been suggested that an apparatus be used for determiningthe radioactivity of a chromatogram in which the chromatogram ispositioned on a rotating cylinder, with the radiation counter located ina fixed position along a diametral plane of the rotating cylinder. Suchapparatus gives satisfactory results only in those cases in which thechromatogram on paper provides substantial radiation at differentpoints. On the contrary, if the quantity of radiation from the surfaceto be examined is small, it is necessary to equip the radiation counterwith a large window so that the radiation measured by the counteremanates not only from the generatrix of the cylinder which is closestto the center of the window of the counter, but also from neighboringpoints, the distance of which from the window is greater than that ofthe generatrix the radiation from which is theoretically being measured.This introduces an error into the measurement since the distance fromthe center of the window to the point of origin of the radiation is notconstant. Moreover, while such an apparatus is easy to use with paperchromatograms, it is not so easy to use with chromatograms on a thinlayer of material between the application of the thin layer to therotating cylinder is apt to tear the thin layer, thus preventing theconvenient effectuation of the desired measurements.

It has also been suggested that an apparatus be provided which permitsthe radioactivity of a chromatogram to be measured and in whichapparatus the radiation counter is stationary and positionedperpendicularly to a moving table which is translated in a directionperpendicular to the axis of the counter. Such a device avoids thetearing of chromatograms formed on a thin layer of material but takes upa good deal of space because the movable table must travel through aspace having a length which is necessarily at least twice the length ofthe chromatogram to be examined.

Moreover, in all the known apparatus, the paper chromatograms aremounted on the movable support which carries them by gripping thembeneath lateral bars which hold the paper along two substantiallyparallel lines. In the first place, it must be emphasized that the twolateral bars must necessarily be satisfactorily parallel to prevent thepaper from buckling so that it is not smoothly applied to its support.Moreover, the gripping of the paper results in the creation of localizedtensions which may result in slight undulations in the paper. It shouldbe emphasized at this point that any undulation in the paper withrespect to its support generates errors in the measurement to beeffected, because it changes the distance between the radioactive point,the radiation of which is to be measured, and the center of the windowof the radiation counter.

It is the purpose of the present invention to provide an apparatus whichmay be used to detect radiation at various points on a chromatogram,which apparatus eliminates the aforesaid disadvantages. The apparatusaccording to the invention may also be advantageously used in fieldsother than the study of chromatograms, in particular, whenever it isnecessary to measure phys ical and/or chemical characteristics atdifferent points of a plane surface being subjected to examination.

It is accordingly an object of the present invention to provide, as anew article of manufacture, an apparatus for the detection andmeasurement of physical and/or chemical characteristics at differentpoints on a surface being examined, said apparatus comprising asupporting table and at least one measuring device, the supporting tableand said at least one measuring device being mounted for relativemovement and characterized by the fact that, in the first place, thesupporting table is stationary and the measuring device or devices istranslated with respect to the supporting table and, in the secondplace, the surface to be examined is attached to the supporting table bymeans of at least one thin member made of a magnetic material, theentire surface of which is adapted to be applied to the flat surface ofthe supporting table, said supporting table being itself made of amagnetic material and constituting one pole of a permanent magnet, theedges of the sheet to be examined being inserted between the thin memberand the supporting table.

In a first embodiment of the invention, the supporting table maycomprise certain transparent zones in alignment with at least one devicefor emitting radiation so as to permit the examination of thetransparency of the sheet being examined while positioned on thesupporting table. In a second embodiment, a measuring device isassociated with a device for emitting radiation, which preferably moveswith said measuring device during its displacements relative to thesurface being examined, which permits the examination of the surface byreflection. In a third embodiment the measuring device receivesradiation or vibrations emitted by the surface being examined whilelying on the supporting table.

The two first embodiments hereinbefore envisaged may advantageously beused for the study of colorimetric densities, brightness, fluorescence,transparency, the study of the state of the surface by an echo system,and the study of the granulametry of the surface being examined. Theradiation used may be light rays in the visible or nonvisible spectrumor alpha, beta or gamma radiation. The vibrations used may in particularbe ultrasonic vibrations.

One example of the third embodiment hereinbefore mentioned relates tothe study of radioactive emissions from different points onchromatograms. In this example, the measuring device. is a radiationcounter and the surface being examined is a chromatogram on paper or ona thin layer of material. In a preferred embodiment of the invention thethin member which holds the surface being examined on the supportingtable consists of a plate having a window for one or more flexiblesheets, with the sheet being examined being preferably held in place bytwo thin members positioned on opposite sides of that portion of thesurface of the sheet which is to be examined. The supporting tableconsists of a plate of ferromagnetic material and carries on its faceremote from the chromatogram permanent magnets, the fields of which allrun in the same direction and substantially perpendicular to thesupporting table. The permanent magnets are discs of ferrite positionedin seats in the surface of the supporting table remote from the materialbeing examined. The supporting table is rectangular in shape and themeasuring device moves parallel to the major axis of the supportingtable. The apparatus comprises a single measuring device which iscarried by mobile means for translating it parallel to a major axis ofthe supporting table. The mobile means which carries the measuringdevice comprises a hinge permitting the axis of the measuring device tobe swung through an angle of substantially 90 about the axis of thehinge. The axis of the hinge of the movable means is parallel to themajor axis of the supporting table. The part of the mobile means whichcan swing around said hinge may take two extreme positions, in one ofwhich it abuts the other part of the mobile means, and the axis of themeasuring device is parallel to the supporting table, and in the secondof which it rests by means of a roller on the supporting table and theaxis of the measuring device is perpendicular to said supporting table.The mobile means, in its movement relative to the table support, isguided by at least one guide bar parallel to the major axis of thesupporting table and is fixed to a nut which cooperates with a threadedrod which is preferably rotated at constant speed through a motor andreduction gearing. This motor, the corresponding transmission, thethreaded drive rod of the mobile means and the guide bar or bars of themobile means, are positioned beneath the supporting table which ismounted on a frame in the form of a parallelopipedic box, with thesupporting table constituting its upper surface. The measuring device isvertically slidable in a cylindrical casing attached to the mobile meansand in actuated by a threaded ring cooperating with threads on the wallof the casing.

In a variation of the preferred embodiment just described, the apparatusaccording to the invention comprises two measuring devices positioned onthe same axis on opposite sides of the supporting table. The supportingtable has, in alignment with the axis of the measuring device positionedbeneath the supporting table, a slot permitting the passage of radiationand/or vibrations from those points on the surface being examined whichare in alignment with said slot. The two measuring devices are carriedby the same mobile means, which is translated with respect to thesupporting table.

In a first improvement, the mobile means may be separated from thethreaded rod which drives it by opening up the nut to which it isattached and which cooperates with said threaded rod. This is preferablyaccomplished by manually separating the two halves of the nut. Suchseparation permits the rapid manual movement of the mobile equipmentwith respect to the table when it is desired to bring the measuringdevice into alignment with a predetermined point on the surface beingexamined. In a variation of this arrangement, in order to achieve thesame result, the motor which normally drives thethreaded rod may beassociated with a clutch, which, when actuated, simultaneously connectsthe threaded rod to another relatively high speed driving motor.

The apparatus which has just been described makes it possible to carryout measurements relative to points on the surface being examined whichare spaced along a line parallel to the axis of translation of themobile means. In a second improvement a course-reversing contact isprovided at the end of the path of travel of the mobile means so as toautomatically permit the desired measurements to be made along the sameline travelled in the reverse direction, either at the same speed, or ata different speed. This improvement makes it possible to obtain asystematic doubling of the number of measurments along each line on thesurface being examined. It is also possible to provide, at the end ofthe path of travel of the mobile means, a contact for stopping saidmobile means.

In a third improvement according to the invention the movement of themeasuring device with respect to the supporting table may be produced,not merely by longitudinal translation of the movable means with respectto said table, but also by the transverse translation of a movablecarriage on the mobile means which carries the measuring means formovement with respect to the mobile means which supports it. Thetransverse translation of the measuring means may be produced by a lowspeed motor attached to the movable carriage, said low speed motordriving a gear which cooperates with a rack fixed to the mobile means.The low speed motor is supplied through a switch positioned at tne endof the path of travel of the mobile means. In a particular case in whichthe apparatus according to the invention relates to the study of theradiation emitted by a chromatogram, the transverse displacement of theradiation counter with respect to the movable means may be carried outby hand, or automatically, as indicated above. The members for holdingthe chromatogram on the supporting table are simply laid on the edges ofsaid chromatogram and are held on the supporting table by the magneticfield of the permanent magnets associated with that table. It is obviousthat the signals provided by the radiation counter may be supplied in aconventional manner to integrating means and/or recording means whichmake is possible to count the measurements effectuated by the counter.Variable and/or adjustable values may be adopted for the speed oftranslation of the counter. It is also possible to equip the supportingtable with millimeter scales which make it possible to locate the pointsin the surface from which the radiation is being detected by thecounter. In a variation, the apparatus according to the inventioncomprises two radiation counters on the same axis positionedsymmetrically with respect to the supporting table, said tablecomprising, in alignment with the axes of these two counters, a slotpermitting the passage of radiation from points on the chromato gramwhich are in alignment with said slot, said two counters being carriedby the same movable means and driven in translation with respect to thesupporting table. This variation makes it possible to improve thefacility of raading in the case of chromatograms on paper because theloss of time due to the measurement of a single side of the paper iseliminated.

It should be noted that, when the device according to the invention isapplied to the examination of a chromatogram, the chromatogram isattached to the supporting table without being squeezed at its edges sothat optimum attachment of the chromatogram is obtained and undulationsof said chromatogram with respect to the supporting table is avoided,thus making it possible to eliminate one of the causes of errors in suchmeasurements. Moreover, the supporting table, being stationary, may haverelatively small dimensions, and in particular, may have a sizesubstantially equal to that of the chromatograms to be analyzed.Finally, since the supporting table is flat, any cracking ofchromatograms formed on thin layers of material is avoided.

In order that the object of the invention may'be better understood twoembodiments thereof will now be described, purely by way of illustrationand example, with reference to the accompanying drawings, in which:

FIG. I is a perspective view showing a first embodiment of a device fordetecting and measuring in accordance with the invention;

FIG. 2 is a section taken along the line II--Il of FIG. 1, showing theaxis of the radiation counter positioned horizontally so that achromatogram may be mounted on the supporting'table;

FIG. 3 is a bottom plan view of the apparatus of FIG.

FIG. 4 is a perspective view of a second embodiment of an apparatusaccording to the invention, also adapted for use in studyingchromatograms;

FIG. 5 is a section taken along the line V-V of FIG. 4, showing the axisof the radiation counter moved to a horizontal position so that achromatogram may be placed on the supporting table; and

FIG. 6 is a schematic perspective view showing the device for operatingthe two halves of the nut and thereby permitting the mobile means to beseparated from the threaded drive rod of the apparatus of FIG. 4.

Referring now to FIGS. 1 to 3, it will be seen that reference numeral 1indicates the rectangular supporting table of the apparatus according tothe invention. The table 1 constitutes the upper part of aparallelopipedic box which serves as the stationary framework of theapparatus. Reference numerals 2a, 2b, 2c and 2d indicate the fourvertical sides of this box, which has no bottom. The side 2b carries onits outer surface a plate 3 which supports the control switches andindicators for controlling the apparatus. The side 2d which is oppositethe side 2b has a longitudinal slot 4 which extends the length of thesupporting table 1. Between the two transverse sides 2a and 2c are twoparallel guides 5 and 6 which serve as crossbars. The plane defined bythe bars 5 and 6 is parallel to the plane of the supporting table 1.I-Ialfway between the bars 5 and 6 is a threaded rod 7 parallel to thetwo bars 5 and 6 and driven in rotation by a chain 8 through a slowspeed motor 9 carried by the side 2b of the framework of the apparatus.Slow speed motor 9 is mounted inside the box defined bythe sides 2a, 2b,2c and 2d and the supporting table 1. Cylindrical seats 10 are formed inthe lower surface of the supporting table 1, which is made of an alloyof the Duralumin type. Discs of ferrite 11 are located in these seatsand constitute permanent magnets. The discs 11 are held in the seats 10by tabs 12. The ends of each tab are in alignment with two adjacentdiscs 11, while the central part of the tab is connected to the lowersurface of the supporting table 1 by a screw 13. Mobile means 14 ismovable with respect to the stationary part of the apparatus constitutedby the supporting table 1 and the sides 2a, 2b, 2c and 2d. The mobilemeans comprises two parts articulated about a hinge, the axis 15 ofwhich is parallel to a major axis of the supporting table.

The lower part of the mobil means is connected to the framework and maybe translated with respect to said framework, whereas the upper part, byreason of its articulation about the axis 15, may be rotated through anangle of with respect to the framework about said axis 15. The lowerpart of the mobile means comprises two crossbars 16 separated from eachother by a nut 17. The two crossbars 16 are perpendicular to the sides2b, 2d of the framework and the nut 17 cooperates with the threaded rod7. The two crossbars 16 are connected to each other at their two endsand pass through the side 2d of the framework via the longitudinal slot4. They are connected to a plate 18 perpendicular thereto which carriesthe shaft 15. The upper part of the mobile means 14 comprises a yoke 19which brackets the plate 18 and is articulated with respect theretoabout the shaft 15. The yoke 19 is attached to two parallel bars 20connected to an end plate 21, the lower part of which carries a roller22 which is adapted to roll on the supporting table 1 when the plane ofthe two bars 20 is parallel to the plane of the supporting table 1. Thetwo transverse bars 20 carry a carriage 23 on which a radiation counterof the Geiger type is mounted. The counter 24 is mounted inside acylinder 24a attached to the carriage 23. A threaded ring 29 is attached-to the counter 24 and the threading on this ring cooperates withthreading carried by the cylinder 24a in order to permit adjustment ofthe height of the counter 24. Transverse sliding of the carriage 23 onthe bars 20 is permitted by longitudinal bearings 25. The position ofthe carriage 23 with respect to the end plate 21 is determined by a lockscrew controlled by a knurled knob 26. The counter 24 has, on thesurface facing the supporting table, a rectangular window, a set ofwindows of different dimensions beingassociated with a single counter24.

When the distribution of the radioactive elements on a chromatogram onpaper is to be examined, the paper 27 of the chromatogram is mountedflat on the supporting table 1 and the edges of this paper are held inplace by positioning a thin steel blade 28 on each of the edges parallelto the major axis of the supporting table 1. The two blades 28 are madeof a ferromagnetic material and attracted to supporting table 1 becauseof the presence of the discs of ferrite 11. The paper 27 is held firmlywithout any squeezing of the paper at its edges so that any undulationof the paper with respect to its support is avoided. When the paper hasbeen positioned on the support 1, the upper part of the mobile means islowered from the position shown in FIG. 2 to the position shown in FIG.1, that is to say until the roller 22 comes into contact with the uppersurface of the supporting table 1. The center of the window of thecounter 24 is then in position at a predetermined vertical distance fromthe paper 27 regardless of which point on the paper is in alignment ofthe counter 24.

The motor is then started by one of the control switches positioned onthe plate 3. Motor 9 drives through a chain 8 the threaded rod 7, whichcooperates with the nut 17 which causes translation of the mobile means14 parallel to the major axis of the supporting table 1. Depending onwhich zone of the paper 27 is to be examined by the counter 24, theposition of the movable carriage 23 is adjusted with respect to the endplate 21. It is obvious that all of the surface of the paper 27 may beprogressively explored by displacing the carriage step by step over theentire width of the supporting table 1.

It will be seen that, in the apparatus according to the invention, it isespecially easy to mount the chromatogram paper 27 on the supportingtable, partly because of the way in which it is held by the thin blades28, and partly because of the possibility of positioning the axis of thecounter 24 horizontally by moving the yoke 19 on the plate 18 to theposition shown in FIG. 2. It should also be noted that the accuracy ofmeasurement of the radiation is improved because of the fact that, inthe first place, any variation in the distance between the paper 27 andthe counter 24 is systematically avoided, and because in the case ofchromatograms on thin layers, there is no risk of deterioration of thelayers since the supporting table 1 is rigorously fiat.

Referring now to FIGS. 3 to 6, it will be seen that the apparatus whichis described is quite similar to the preceding embodiment. For thoseelements of this second apparatus which are identical to those of thefirst embodiment the same reference numerals have been used. For thedetails of such similar elements reference should be made to thepreceding description. On the lower surface of the supporting table 1 ofthis second embodiment discs of ferrite 11 constituting permanentmagnets have been positioned. Inside the supporting table 1 are twoguidebars 5 and 6 parallel to the major axis of the table and a threadedrod 7 positioned be tween the said two bars. The rod 7 is driven inrotation through a chain 8 by a slow speed motor. The mobile means 14comprises two parts which are articulated about a hinge, the axis 15 ofwhich is parallel to the major axis of the supporting table 1. The lowerpart of the mobile means connected to the framework may be translatedwith respect thereto while the upper part, because of its articulationabout the axis 15 may be rotated through an angle of 90 with respect tothe framework carrying said axis 15.

The lower part of the mobile means comprises two crossbars 16 connectedto each other and embracing two half nuts 17a, 17b, constituting a nutcooperating with the threaded rod 7. These two half nuts 17a, 17b mayslide parallel to the center line between the two crossbars 16 whileguided by slideways carried by the crossbars. The half nut 17b is fixedto a rod 101 adapted to be translated parallel to the minor axis of thesupporting table by a rod 102 which may be rotated by a handle 103. Rod102 is translated with the rod 101 but may rotate with respect thereto.The rods 101 and 102 are co-axial. The rod 102 carries a pawl 104 whichcooperates with a helical cam attached to the supporting table 1. Therod 102 carries a stop washer 106 biased by a spring 107 which bears atone end on the lateral part of the framework. The half nut 17b is fixedto a vertical arm 108b, whereas the half screw 17a is fixed to avertical arm 108a. The two arms 108a and 108b are pivotally connected attheir other ends to two ends of a lever 109. The lever 109 is adapted torotate about a shaft 1 10 carried by the crossbar 16 of the mobile means14. When the user grasps the end of 103 and rotates the rod 102 aboutits axis the rods 101 and 102 are translated parallel to the minor axisof the supporting table by reason of the cooperation between the pawl104 and the helical cam 105. Contact between the pawl and the ramp ismaintained by the helical spring 107. When the handle 103 is in theposition shown in solid lines on FIGS. 2 and 3 the two half nuts 17a and17b have their lower edges positioned against each other and the nutwhich they form may cooperate with the threaded rod 7. On the contrary,if the handle 103 is turned to bring it into the position shown inbroken lines on FIGS. 2 and 3, the rod 101 is translated so as toseparate from the threaded rod 7, which also separates the half nut 17bconnected thereto and, through the lever 109 separates the half nut 17aon the opposite side. The two half nuts 17a and 17b slide in groovesprovided for this purpose in the two bars 16 of the mobile means 14. Theupper part of the mobile means 14 comprises two transverse guidebars20a, 20b. The bar 20a is cylindrical and the bar 20b has a half flatperpendicular to the supporting table 1 opposite the bar 20a. On thishalf flat of the bar 20b is a rack (not shown on the drawing) whichcooperates with a gear carried by a low speed motor 112 positioned onthe movable carriage 23 which may be displaced transversely along thebars 20a, 20b of the mobile means 14. The movable carriage 23 alsocarries a radiation counter 24 slidable with respect to a cylindercarried by the carriage 23. The counter 24 is fixed to a threaded ring29. The threads on the ring 29 cooperate with threads carried by saidcylinder in order to permit regulation of the height of the counter 24.The movable carriage 23 carries' a pointer 113 which moves in alignmentwith a scale 114 carried by the movable member 14. The scale 1 14 isparallel to the minor axis of the supporting table 1. At the edge of thesupporting table 1 a graduated scale 115 is inlaid into the supportingtable, with one end of the ruler 114 in alignment with the scale 115.Adjacent the two transverse edges of the supporting table 1 are twopairs of vertical tabs 116 which support a rod 117 at each end of thetable. Each rod 117 has positioned thereon at least one microswitch 118transverse position of which is adjustable. This microswitch is adaptedto cooperate with a member on the mobile means when said mobile meanshas reached the end of its path of travel with respect to the supportingtable. The surface to be examined, in the present case a chromatogram onpaper, is mounted on the supporting table 1 by means of twoferromagnetic blades 28. The apparatus which has just been describedoperates in substantially the same manner as the first embodimentdescribed in connection with FIGS. 1 to 3. However, when it is desiredto move the mobile means 14 rapidly in order to position the window ofthe counter 24 above a predetermined point on the chromatogram 27, itsuffices to actuate the handle 103 to separate the two halfnuts 17a, 17band then displace the mobile means 14 by sliding it along the guidebars5 and 6. The mobile means 14 may be driven through the threaded rod 7 byrotating the handle 103 in the opposite direction. This brings the twohalf-nuts 17a, 17b back together around the threaded rod 7.

When it is desired to automatically scan the entire surface of thechromatogram 27 the microswitch 118 positioned at the end of the path oftravel of the movable means 14 is connected to actuate a low speed motor112 for a predetermined time. This, acting through the gear of the slowspeed motor 112 and the corresponding rack, causes transversedisplacement of the movable carriage 23 which slides on the bars 20a and20b. This transverse displacement has a value which is a function of thetime of rotation of the low speed motor 112. There is thus provided, inautomatic sequence, movement of the movable member 14, the

direction of rotation of the threaded rod 7 having been reversed bymeans of a microswitch 118 positioned at the end of the path of travel,or by the same microswitch which has just actuated the low speed motor112. It will be seen that it is thus possible to scan the entire surfaceof the chromatogram 27 in a single completely automatic operation.

The existence of the scales 114 and 115 makes it possible to locate withprecision the position of a zone on the chromatogram 27 and examine thiszone selectively by bringing the movable means into position afterhaving separated the two half-nuts 17a, 17b, as previously described. Itwill of course be appreciated that the embodiments which have just beendescribed have been given purely by way of illustration and example, andmay be modified as to detail without thereby departing from the basicprinciples of the invention. In particular, in the first embodimenthereinbefore described, the threaded ring 29 may have a very low pitchand be graduated to permit the precise regulation of the distancebetween the window of the counter and the chromatogram.

What is claimed is:

1. Apparatus for the detection and measurement of the characteristics ofa surface, said apparatus comprising a stationary, magnetized supportingtable,- at least one measuring device mounted for translation withrespect to said supporting table, and at least one thin member made of amagnetic material positioned on said supporting table to hold a sheethaving a surface to be examined with the edge of said sheet insertedbetween the thin member and the supporting table.

2. Apparatus as claimed in claim 1 in which the supporting tablecomprises several transparent zones in alignment with at least oneradiation emitting means positioned therebeneath to permit examinationof the transparency of the surface being examined while positioned onsaid supporting table.

3. Apparatus as claimed in claim 1 in which the measuring means isassociated with radiation means mounted to move with said measuringmeans parallel to the surface of said supporting table to permitexamination of the surface to be examined by reflection.

4. Apparatus as claimed in claim 1 in which the measuring means isresponsive to radiations emitted by the surface to be examined.

5. Apparatus as claimed in claim 4 in which the surface to be examinedis a chromatogram, and said measuring device is a radiation counter ofthe Geiger type.

6. Apparatus as claimed in claim 1 in which said at least one thinmember comprises a pair of flexible blades adapted to be positionedalong two opposite edges of the surface to be examined.

7. Apparatus as claimed in claim 1 in which the supporting table is aplate of ferro-magnetic material which carries on the face remote fromthe surface to be examined permanent magnets having parallel fieldssubstantially perpendicular to the surface'of the supporting table.

8. Apparatus as claimed in claim 7 in which the permanent magnets of thesupporting table are discs of ferrite positioned in seats in the surfaceof the supporting table remote from the surface carrying the sheet to beexamined. I

9. Apparatus as claimed'in claim 1 in which the supporting table issubstantially rectangular and comprisit) ing a single measuring devicewhich is translated parallel to the major axis of the supporting table.

10. Apparatus as claimed in claim 9 in which the measuring means iscarried by mobile means mounted for translation parallel to the majoraxis of the supporting table.

11. Apparatus as claimed in claim 10 in which the mobile means whichcarries the measuring means comprises a hinge permitting said measuringmeans to be rotated through an angle of substantially about the axis ofsaid hinge.

12. Apparatus as claimed in claim 11 in which the axis of the hinge ofthe mobile means is parallel to the major axis of the supporting table.

13. Apparatus as claimed in claim 11 in which said measuring means isrotatable about the axis of said hinge between two positions in thefirst of which it is clear of the supporting table with the axis of themeasuring device parallel to the supporting table and in the second ofwhich it rests through a roller on the supporting table with the axis ofthe measuring means perpendicular to said supporting table.

14. Apparatus as claimed in claim 10 in which said mobile means isguided for translation relative to said supporting table by at least oneguide bar parallel to a major axis of the supporting table and isattached to a nut which cooperates with a threaded rod rotatably drivenat constant speed by a low speed motor.

15. Apparatus as claimed in claim 14 in which the low speed motor, atransmission therefrom, the threaded driving rod of the mobile means,and the guide bar of the mobile means are positioned beneath thesupporting table, said supporting table being mounted on a framework inthe form of a parallelopipedic box with the supporting tableconstituting the upper surface of said box.

16. Apparatus as claimed in claim 10 in which the radiation counter isvertically slidable in a sheath carried by the mobile means and ismounted to move with a ring having threads cooperating with threads onthe inner wall of the sheath.

17. Apparatus as claimed in claim 1 which comprises measuring meansmounted coaxially on opposite sides of the supporting table, saidsupporting table comprising, in alignment with the axis of the measuringmeans positioned beneath the supporting table, a slot for permitting thepassage of radiation to a point on the surface being examined inalignment with said slot, both said measuring means being carried by thesame mobile means fortranslation relative to said supporting table.

18. Apparatus as claimed in claim 14 in which said nut is in two partsand comprising manually operable means for separating the mobile meansfrom the threaded rod by separating the parts of said nut.

'19. Apparatus as claimed in claim 14 in which the low speed drivingmotor for the threaded rod is associated with a clutch which, whenactuated, simultaneously connects the threaded rod to be driven byanother high speed motor.

20. Apparatus as claimed in'claim 10 in which the mobile means comprisesat least onetransverse guide member along which a movable carriagesupporting a measuring device travels. v

21. Apparatus as claimed in claim 20 in which the movable carriagecarries a low speed motor driving a gear which cooperates with a rack ona transverse guide member on the mobile means.

I member of which cooperates with a stationary recording sheet, one ofthe coordinates of the recording curve corresponding to the displacementof the mobile means parallel to a major axis of the support while theother coordinate corresponds to the result of the measurement obtainedfrom the measuring means carried by the mobile means.

24. Apparatus as claimed in claim 10 comprising a limit switch at theend of the path of travel of said mo bile means, which switch isconnected to one of said motors to initiate a predetermined operation bythat motor when said switch is actuated.

1. Apparatus for the detection and measurement of the characteristics ofa surface, said apparatus comprising a stationary, magnetized supportingtable, at least one measuring device mounted for translation withrespect to said supporting table, and at least one thin member made of amagnetic material positioned on said supporting table to hold a sheethaving a surface to be examined with the edge of said sheet insertedbetween the thin member and the supporting table.
 2. Apparatus asclaimed in claim 1 in which the supporting table comprises severaltransparent zones in alignment with at least one radiation emittingmeans positioned therebeneath to permit examination of the transparencyof the surface being examined while positioned on said supporting table.3. Apparatus as claimed in claim 1 in which the measuring means isassociated with radiation means mounted to move with said measuringmeans parallel to the surface of said supporting table to permitexamination of the surface to be examined by reflection.
 4. Apparatus asclaimed in claim 1 in which the measuring means is responsive toradiations emitted by the surface to be examined.
 5. Apparatus asclaimed in claim 4 in which the surface to be examined is achromatogram, and said measuring device iS a radiation counter of theGeiger type.
 6. Apparatus as claimed in claim 1 in which said at leastone thin member comprises a pair of flexible blades adapted to bepositioned along two opposite edges of the surface to be examined. 7.Apparatus as claimed in claim 1 in which the supporting table is a plateof ferro-magnetic material which carries on the face remote from thesurface to be examined permanent magnets having parallel fieldssubstantially perpendicular to the surface of the supporting table. 8.Apparatus as claimed in claim 7 in which the permanent magnets of thesupporting table are discs of ferrite positioned in seats in the surfaceof the supporting table remote from the surface carrying the sheet to beexamined.
 9. Apparatus as claimed in claim 1 in which the supportingtable is substantially rectangular and comprising a single measuringdevice which is translated parallel to the major axis of the supportingtable.
 10. Apparatus as claimed in claim 9 in which the measuring meansis carried by mobile means mounted for translation parallel to the majoraxis of the supporting table.
 11. Apparatus as claimed in claim 10 inwhich the mobile means which carries the measuring means comprises ahinge permitting said measuring means to be rotated through an angle ofsubstantially 90* about the axis of said hinge.
 12. Apparatus as claimedin claim 11 in which the axis of the hinge of the mobile means isparallel to the major axis of the supporting table.
 13. Apparatus asclaimed in claim 11 in which said measuring means is rotatable about theaxis of said hinge between two positions in the first of which it isclear of the supporting table with the axis of the measuring deviceparallel to the supporting table and in the second of which it reststhrough a roller on the supporting table with the axis of the measuringmeans perpendicular to said supporting table.
 14. Apparatus as claimedin claim 10 in which said mobile means is guided for translationrelative to said supporting table by at least one guide bar parallel toa major axis of the supporting table and is attached to a nut whichcooperates with a threaded rod rotatably driven at constant speed by alow speed motor.
 15. Apparatus as claimed in claim 14 in which the lowspeed motor, a transmission therefrom, the threaded driving rod of themobile means, and the guide bar of the mobile means are positionedbeneath the supporting table, said supporting table being mounted on aframework in the form of a parallelopipedic box with the supportingtable constituting the upper surface of said box.
 16. Apparatus asclaimed in claim 10 in which the radiation counter is verticallyslidable in a sheath carried by the mobile means and is mounted to movewith a ring having threads cooperating with threads on the inner wall ofthe sheath.
 17. Apparatus as claimed in claim 1 which comprisesmeasuring means mounted coaxially on opposite sides of the supportingtable, said supporting table comprising, in alignment with the axis ofthe measuring means positioned beneath the supporting table, a slot forpermitting the passage of radiation to a point on the surface beingexamined in alignment with said slot, both said measuring means beingcarried by the same mobile means for translation relative to saidsupporting table.
 18. Apparatus as claimed in claim 14 in which said nutis in two parts and comprising manually operable means for separatingthe mobile means from the threaded rod by separating the parts of saidnut.
 19. Apparatus as claimed in claim 14 in which the low speed drivingmotor for the threaded rod is associated with a clutch which, whenactuated, simultaneously connects the threaded rod to be driven byanother high speed motor.
 20. Apparatus as claimed in claim 10 in whichthe mobile means comprises at least one transverse guide member alongwhich a movable carriage supporting a measuring device travels. 21.Apparatus as claimed in claim 20 in which tHe movable carriage carries alow speed motor driving a gear which cooperates with a rack on atransverse guide member on the mobile means.
 22. Apparatus as claimed inclaim 10 in which the supporting table has a first graduated scaleparallel to the major axis of said table and the mobile means has asecond graduated scale parallel to the minor axis of the table, saidsecond scale having preferably a zone in alignment with the first scaleand index means being mounted on the measuring device and positioned inalignment with the second scale.
 23. Apparatus as claimed in claim 10 inwhich the mobile means is attached to a recorder the marking member ofwhich cooperates with a stationary recording sheet, one of thecoordinates of the recording curve corresponding to the displacement ofthe mobile means parallel to a major axis of the support while the othercoordinate corresponds to the result of the measurement obtained fromthe measuring means carried by the mobile means.
 24. Apparatus asclaimed in claim 10 comprising a limit switch at the end of the path oftravel of said mobile means, which switch is connected to one of saidmotors to initiate a predetermined operation by that motor when saidswitch is actuated.